[PATCH] clocksource: dw_apb_timer_of: support timer-based delay

Jisheng Zhang
2015-11-02T02:51:13Z

Dear Daniel,

On Fri, 30 Oct 2015 13:37:01 +0100
Daniel Lezcano wrote:

> On 10/30/2015 12:09 PM, Jisheng Zhang wrote:
> > Dear Daniel,
> >
> > On Fri, 30 Oct 2015 11:44:46 +0100
> > Daniel Lezcano <daniel.lezcano@....> wrote:
> >
> >> On 10/30/2015 09:27 AM, Jisheng Zhang wrote:
> >>> Implement an ARM delay timer to be used for udelay(). This allows us to
> >>> skip the delay loop calibration at boot on Marvell BG2, BG2Q, BG2CD
> >>> platforms. And after this patch, udelay() will be unaffected by CPU
> >>> frequency changes.
> >>>
> >>> Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
> >>> ---
> >>> drivers/clocksource/Kconfig | 10 ++++++++++
> >>> drivers/clocksource/dw_apb_timer_of.c | 16 ++++++++++++++++
> >>> 2 files changed, 26 insertions(+)
> >>>
> >>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> >>> index a7726db..7b081805 100644
> >>> --- a/drivers/clocksource/Kconfig
> >>> +++ b/drivers/clocksource/Kconfig
> >>> @@ -29,6 +29,16 @@ config DW_APB_TIMER_OF
> >>> select DW_APB_TIMER
> >>> select CLKSRC_OF
> >>>
> >>> +config DW_APB_TIMER_BASED_DELAY
> >>> + bool "DW APB timer based delay"
> >>> + depends on ARM && DW_APB_TIMER_OF
> >>> + default n
> >>> + help
> >>> + This option enables support for using the DW APB timer to
> >>> + implement timer-based delay. It is useful for skiping the
> >>> + delay loop calibration at boot on some platforms. And the
> >>> + udelay() will be unaffected by CPU frequency changes.
> >>> +
> >>
> >> Why do you want it to be optional ?
> >>
> >
> > Because in some platforms which has arm arch timer, this dw apb timer
> > delay isn't needed, the arch timer is better. So we want it be optional
> > so that the platforms which need this feature select it manually when config
> > the kernel.
>
> Correct me if I am wrong. If you have the arch timer, you don't need the

Yes, I don't need the dw apb timer if we have arch timer,

> dw apb timer at all, no ? So the selection would be arch arm timer *or*
> dw_apb_timer ? not arch_arm_timer for delay and dw_apb_timer for
> clockevents, right ?

Yes, if we have arch timer, I prefer to use it for clockevent and delay.

Could you please provide suggestion how to handle this case?

Thanks,
Jisheng